Many communication systems utilize high performance cables normally having four pairs or more that typically consist of two twisted pairs transmitting data and two receiving data as well as the possibility of four or more pairs multiplexing in both directions. A twisted pair is a pair of conductors twisted about each other. A transmitting twisted pair and a receiving twisted pair often form a subgroup in a cable having four twisted pairs. High-speed data communications media in current usage includes pairs of wire twisted together to form a balanced transmission line. Optical fiber cables may include such twisted pairs or replace them altogether with optical transmission media (fiber optics).
When twisted pairs are closely placed, such as in a communications cable, electrical energy may be transferred from one pair of a cable to another. Energy transferred between conductor pairs is undesirable and referred to as crosstalk. The Telecommunications Industry Association and Electronics Industry Association have define standards for crosstalk, including TIA/EIA-568 A, B, and C including the most recent edition of the specification. The International Electrotechnical Commission has also defined standards for data communication cable crosstalk, including ISO/IEC 11801. One high-performance standard for 100 MHz cable is ISO/IEC 11801, Category 5. Additionally, more stringent standards are being implemented for higher frequency cables including Category 6 and Category 7, which includes frequencies of 200 and 600 MHz, respectively and the most recent proposed industrial standard raising the speeds to 10 Gbit over copper with Ethernet or other cable designs. Industry standards cable specifications and known commercially available products are listed in Table 1 and a set of updated standards for Category 6, including alien crosstalk proposals are included in Tables 2 A–G.
TABLE 1INDUSTRY STANDARD CABLE SPECIFICATIONSTIA CAT 6ANIXTER XP6ANIXTER XP7ALL DATA ATDRAFT 10R3.00XPR3.00XP100 MHzTIA CAT 5eNov. 15, 200111/0011/00MAX TEST100MHz250MHz250MHz350MHzFREQUENCYATTENTUATION22.0db19.8db21.7db19.7dbPOWER SUM32.3db42.3db34.3db44.3dbNEXTACR13.3db24.5dbPOWER SUM10.3db22.5db12.6db23.6dbACRPOWER SUM20.8db24.8db23.8db25.8dbELFEXTRETURN LOSS20.1db20.1db21.5db22.5db
TABLE 2AReturn Loss Requirements for Category 6 CableReturn loss @ 20° C. ± 3° C. (68° F. ± 5.5° F.),worst pair for a length of 100 m (328 ft)Frequency MHzCategory 6 dB 1 ≦ f ≦ 1020 + 5 log (f)10 ≦ f ≦ 2025 20 ≦ f ≦ 25025 − 7 log (f/20)
TABLE 2BInsertion Loss Requirements for Category 6 CableInsertion loss @ 20° C. ± 3° C. (68° F. ± 5.5° F.),worst pair for a length of 100 m (328 ft)Frequency MHzCategory 6 dB.7721.810.06.0250.032.8
TABLE 2CNear End Crosstalk RequirementsFor Category 6 CableHorizontal cable NEXT loss @ 20° C. ± 3° C. (68° F. ± 5.5° F.),worst pair-to-pair, for a length of 100 m (328 ft)Frequency MHzCategory 6 dB0.15086.710.059.3250.038.3
TABLE 2DPower Sum Near End Crosstalk Requirements for Category 6 CablePSNEXT loss @ 20° C. ± 3° C. (68° F. ± 5.5° F.),for a length of 100 m (328 ft)Frequency MHzCategory 6 dB0.15084.710.057.3250.036.3
TABLE 2EEqual Level Near End Crosstalk Requirements for Category 6 CableELNEXT loss @ 20° C. ± 3° C. (68° F. ± 5.5° F.),worst pair-to-pair for a length of 100 m (328 ft)Frequency MHzCategory 6 dB.77270.010.047.8250.019.8
TABLE 2FPower Sum Equal Level Near End Crosstalk Requirementsfor Category 6 CablePSELNEXT loss @ 20° C. ± 3° C. (68° F. ± 5.5° F.),for a length of 100 m (328 ft)Frequency MHzCategory 6 dB.77267.010.044.8250.016.8
TABLE 2GProposed Requirements for Alien Near-end Cross-talk forCategory 6 CableProposed Requirement for Channel Power Sum Alien Near-End Cross-talkFrequencyCategory 6 dBPSANEXT ≧ 60 − 10log(f) 1 ≦ f ≦ 100 MHzPSANEXT ≧ 60 − 15log(f)100 ≦ f ≦ 625 MHz
In conventional cable, each twisted pair of conductors for a cable has a specified distance between twists along the longitudinal direction. That distance is referred to as the pair lay. When adjacent twisted pairs have the same pair lay and/or twist direction, they tend to lie within a cable more closely spaced than when they have different pair lays and/or twist direction. Such close spacing increases the amount of undesirable cross-talk that occurs. Therefore, in many conventional cables, each twisted pair within the cable has a unique pair lay in order to increase the spacing between pairs and thereby to reduce the cross-talk between twisted pairs of a cable. Twist direction may also be varied. Along with varying pair lays and twist directions, individual solid metal or woven metal air shields can be used to electro-magnetically isolate pairs from each other or isolate the pairs from the cable jacket.
Shielded cable, although exhibiting better cross-talk isolation, is more difficult, time consuming and costly to manufacture, install, and terminate. Individually shielded pairs must generally be terminated using special tools, devices and techniques adapted for the job, also increasing cost and difficulty.
One popular cable type meeting the above specifications is Unshielded Twisted Pair (UTP) cable. Because it does not include shielded pairs, UTP is preferred by installers and others associated with wiring building premises, as it is easily installed and terminated. However, UTP fails to achieve superior cross-talk isolation such as required by the evolving higher frequency standards for data and other state of the art transmission cable systems, even when varying pair lays are used.
Some cables have used supports in connection with twisted pairs. These cables, however, suggest using a standard “X”, or “+” shaped support, hereinafter both referred to as the “X” support. Protrusions may extend from the standard “X” support. The protrusions of these prior inventions have exhibited substantially parallel sides.
The document, U.S. Pat. No. 3,819,443, hereby incorporated by reference, describes a shielding member comprising laminated strips of metal and plastics material that are cut, bent, and assembled together to define radial branches on said member. It also describes a cable including a set of conductors arranged in pairs, said shielding member and an insulative outer sheath around the set of conductors. In this cable the shielding member with the radial branches compartmentalizes the interior of the cable. The various pairs of the cable are therefore separated from each other, but each is only partially shielded, which is not so effective as shielding around each pair and is not always satisfactory.
The solution to the problem of twisted pairs lying too closely together within a cable is embodied in three U.S. Pat. Nos. 6,150,612 to Prestolite, 5,952,615 to Filotex, and 5,969,295 to CommScope incorporated by reference herein, as well as an earlier similar design of a cable manufactured by Belden Wire & Cable Company as product number 1711A. The prongs or splines in the Belden cable provide superior crush resistance to the protrusions of the standard “X” support. The superior crush resistance better preserves the geometry of the pairs relatives to each other and of the pairs relative to the other parts of the cables such as the shield. In addition, the prongs or splines in this invention preferably have a pointed or slightly rounded apex top which easily accommodates an overall shield. These cables include four or more twisted pair media radially disposed about a “+”-shaped core. Each twisted pair nests between two fins of the “+”-shaped core, being separated from adjacent twisted pairs by the core. This helps reduce and stabilize crosstalk between the twisted pair media. U.S. Pat. No. 5,789,711 to Belden describes a “star” separator that accomplishes much of what has been described above and is also herein incorporated by reference.
However, these core types can add substantial cost to the cable, as well as excess material mass which forms a potential fire hazard, as explained below, while achieving a crosstalk reduction of typically 3 dB or more. This crosstalk value is based on a cable comprised of a fluorinated ethylene-propylene (FEP) conductors with PVC jackets as well as cables constructed of FEP jackets with FEP insulated conductors. Cables where no separation between pairs exist will exhibit smaller cross-talk values. When pairs are allowed to shift based on “free space” within the confines of the cable jacket, the fact that the pairs may “float” within a free space can reduce overall attenuation values due to the ability to use a larger conductor to maintain 100 ohm impedance. The trade-off with allowing the pairs to float is that the pair of conductors tend to separate slightly and randomly. This undesirable separation contributes to increased structural return loss (SRL) and more variation in impedance. One method to overcome this undesirable trait is to twist the conductor pairs with a very tight lay. This method has been proven impractical because such tight lays are expensive and greatly limits the cable manufacturer's throughput and overall production yield. An improvement included by the present invention to structural return loss and improved attenuation is to provide grooves within channels for conductor pairs such that the pairs are fixedly adhered to the walls of these grooves or at least forced within a confined space to prevent floating simply by geometric configuration. This configuration is both described here within and referenced in U.S. Pat. No. 6,639,152 filed Aug. 25, 2001 as well as PCT/US02/13831 filed at the United States Patent and Trademark Office on May 1, 2002.
A “rifling” or “ladder-like” separator design also contributes to improved attenuation, power sum NEXT (near end cross talk), power sum ACR (attenuation cross-talk ratio) and ELFEXT (equal level far end cross-talk) by providing for better control of spacing of the pairs, adding more air-space, and allowing for “pair-twinning” at different lengths. Additional benefits include reduction of the overall material mass required for conventional spacers, which contributes to flame and smoke reduction.
In building designs, many precautions are taken to resist the spread of flame and the generation of and spread of smoke throughout a building in case of an outbreak of fire. Clearly, the cable is designed to protect against loss of life and also minimize the costs of a fire due to the destruction of electrical and other equipment. Therefore, wires and cables for building installations are required to comply with the various flammability requirements of the National Electrical Code (NEC) in the U.S. as well as International Electrotechnical Commission (EIC) and/or the Canadian Electrical Code (CEC).
A broad range of electrical conductors and electrical cables are installed in modern buildings for a wide variety of uses. Such uses include data transmission between computers, voice communications, as well as control signal transmission for building security, fire alarm, and temperature control systems. These cable networks extend throughout modern office and industrial buildings, and frequently extend through the space between the dropped ceiling and the floor above. Ventilation system components are also frequently extended through this space for directing heated and chilled air to the space below the ceiling and also to direct return air exchange. The space between the dropped ceiling and the floor above is commonly referred to as the plenum area. Electrical conductors and cables extending through plenum areas are governed by special provisions of the National Electric Code (“NEC”).
Cables intended for installation in the air handling spaces (i.e. plenums, ducts, etc.) of buildings are specifically required by NEC/CEC/IEC to pass the flame test specified by Underwriters Laboratories Inc. (UL), UL-910, or its Canadian Standards Association (CSA) equivalent, the FT6. The UL-910, FT-6, and the NFPA 262 represent the top of the fire rating hierarchy established by the NEC and CEC respectively. Also important are the UL 1666 Riser test and the IEC 60332-3C and D flammability criteria. Cables possessing these ratings, generically known as “plenum” or “plenum rated” or “riser” or “riser rated”, may be substituted for cables having a lower rating (i.e. CMR, CM, CMX, FT4, FTI or their equivalents), while lower rated cables may not be used where plenum or riser rated cables are required.
In 1975, the NFPA recognized the potential flame and smoke hazards created by burning cables in plenum areas, and adopted in the NEC a standard for flame retardant and smoke suppressant cables. This standard, commonly referred to as “the Plenum Cable Standard”, permits the use of cable without conduit, so long as the cable exhibits low smoke and flame retardant characteristics. The test method for measuring these characteristics is commonly referred to as the Steiner Tunnel Test. The Steiner Tunnel Test has been adapted for the burning of cables according to the following test protocols: NFPA 262, Underwriters Laboratories (U.L.) 910, or Canadian Standards Association (CSA) FT-6. The test conditions for each of the U.L. 910 Steiner Tunnel Test, CSA FT-6, and NFPA 262 are as follows: a 300,000 BTU/hour flame is applied for 20 minutes to ten 24-foot lengths of test cables mounted on a horizontal tray within a tunnel. The criteria for passing the Steiner Tunnel Test are as follows:
A. Flame spread—flame travel less than 5.0 feet.
B. Smoke Generation:
1. Maximum optical density of smoke less than 0.5.
2. Average optical density of smoke less than 0.15.
Because of concerns that flame and smoke could travel along the extent of a plenum area in the event the electrical conductors and cable were involved in a fire, the National Fire Protection Association (“NFPA”) has developed a standard to reduce the amount of flammable material incorporated into insulated electrical conductors and jacketed cables. Reducing the amount of flammable material would, according to the NFPA, diminish the potential of the insulating and jacket materials from spreading flames and evolving smoke to adjacent plenum areas and potentially to more distant and widespread areas throughout a building.
The products of the present invention have also been developed to support the evolving NFPA standard referenced as NFPA 255 entitled “Limited Combustible Cables” with less than 50 as a maximum smoke index and/or NFPA 259 entitled “Heat of Combustion” which includes the use of an oxygen bomb calorimeter that allows for materials with less than 3500 BTU/lb. for incorporation into the newer cable (and conductors and separators within these cables) designs. The proposed materials of the present invention are for inclusion with high performance support separators and conduit tubes designed to meet the new and evolving standards proposed for National Electrical Code (NEC) adoption in 2005. Table 4 below provides the specific requirements for each of the
Cables conforming to NEC/CEC/IEC requirements are characterized as possessing superior resistance to ignitability, greater resistant to contribute to flame spread and generate lower levels of smoke during fires than cables having lower fire ratings. Often these properties can be anticipated by the use of measuring a Limiting Oxygen Index (LOI) for specific materials used to construct the cable. Conventional designs of data grade telecommunication cable for installations in plenum chambers have a low smoke generating jacket material, e.g. of a specially filled PVC formulation or a fluoropolymer material, surrounding a core of twisted conductor pairs, each conductor individually insulated with a fluorinated insulation layer. Cable produced as described above satisfies recognized plenum test requirements such as the “peak smoke” and “average smoke” requirements of the Underwriters Laboratories, Inc., UL910 Steiner tunnel test and/or Canadian Standards Association CSA-FT6 (Plenum Flame Test) while also achieving desired electrical performance in accordance with EIA/TIA-568 A, B, and C for high frequency signal transmission.
The newer standards are forcing industrial “norms” to change and therefore require a new and unique set of materials that will be required to achieve new standards. These materials are the subject of the present invention and include nano-composites of clay and other inorganics such as ZnO and TiO2 both also as nano-sized particles. In addition, the use of insulative or semi-conductive Buckminster fullerenes and doped fullerenes of the C60 family and the like are part of the present invention and offer unique properties that allow for maintaining electrical integrity as well as providing the necessary reduction in flame retardance and smoke suppression.
While the above described conventional cable, due in part to their use of fluorinated polymers, meets all of the above design criteria, the use of fluorinated polymers is extremely expensive and may account for up to 60% of the cost of a cable designed for plenum usage. A solid core of these communications cables contributes a large volume of fuel to a potential cable fire. Forming the core of a fire resistant material, such as with FEP (fluorinated ethylene-propylene), is very costly due to the volume of material used in the core, but it should help reduce flame spread over the 20 minute test period. Reducing the mass of material by redesigning the core and separators within the core is another method of reducing fuel and thereby reducing smoke generation and flame spread. For the commercial market in Europe, low smoke fire retardant polyolefin materials have been developed that will pass the EN (European Norm) 502666-Z-X Class B relative to flame spread, total heat release, related heat release, and fire growth rate. Prior to this inventive development, standard cable constructions requiring the use of the aforementioned expensive fluorinated polymers, such as FEP, would be needed to pass this rigorous test. Using low smoke fire retardant polyolefins for specially designed separators used in cables that meet the more stringent electrical requirements for Categories 6 and 7 and also pass the new norm for flammability and smoke generation is a further subject of this invention. Tables 3A, 3B, and 4 indicates categories for flame and smoke characteristics and associated test methods as discussed above.
TABLE 3AInternational Classification and Flame Test Methodology for Communications CableAdditionalClassTest MethodsClassification CriteriaClassificationAcaEN ISO 1716PCS ≦ 2.0 MJ/kg (1) andPCS ≦ 2.0 MJ/kg (2)B1caFIPEC20 Scenario 2 (6)FS ≦ 1.75 m andSmoke production (3, 7)andTHR1200 ≦ 10 MJ andand FlamingPeak HRR ≦ 20 kW anddroplets/particles (4)FIGRA ≦ 120 Ws−1and Acidity (5)EN 50285-2-1H ≦ 425 mmB2caFIPEC20 Scenario 1 (6)FS ≦ 1.5 m andSmoke production (3, 8)andTHR1200 ≦ 15 MJ andand FlamingPeak HRR ≦ 30 kW anddroplets/particles (4)FIGRA ≦ 150 Ws−1and Acidity (5)EN 50285-2-1H ≦ 425 mmCcaFIPEC20 Scenario 1 (6)FS ≦ 2.0 m andSmoke production (3, 8)andTHR1200 ≦ 30 MJ andand FlamingPeak HRR ≦ 60 kW anddroplets/particles (4)FIGRA ≦ 300 Ws−1and Acidity (5)EN 50285-2-1H ≦ 425 mmDcaFIPEC20 Scenario 1 (6)THR1200 ≦ 70 MJ andSmoke production (3, 8)andPeak HRR ≦ 400 kW andand FlamingFIGRA ≦ 1300 Ws−1droplets/particles (4)and Acidity (5)EN 50285-2-1H ≦ 425 mmEcaEN 50285-2-1H ≦ 425 mmAcidity (5)FcaNo Performance Determined(1) For the product as a whole, excluding metallic materials.(2) For any external component (ie. Sheath) of the product.(3) S1 = TSP1200 ≦ 50 M2 and peak SPR ≦ 0.25 m2/s S2 = TSP1200 ≦ 400 M2 and peak SPR ≦ 1.5 m2/s S3 = Not S1 or S2(4) For FIPEC20 Scenarios 1 and 2: d0 = No flaming droplets/particles within 1200 s d1 = No flaming droplets/particles persisting longer than 10 s within 1200 s d3 = not d0 or d1(5) EN 50285-2-1: (?) A1 = conductivity < 2.5 μS/mm and pH > 4.3 A2 = conductivity < 10 μS/mm and pH > 4.3 A3 = not A1 or A2 No declaration = No Performance Determined(6) Airflow into chamber shall be set to 8000 +/− 800 l/min. FIPEC20 Scen.1 = prEN50399-2-1 with mounting and fixing according to Annex 2 FIPEC20 Scen.2 = prEN50399-2-2 with mounting and fixing according to Annex 2(7) The smoke class declared in class B1ca cables must originate from the FIPEC20 Scen.2 test(8) The smoke class declared in class B2ca cables must originate from the FIPEC20 Scen.1 test
TABLE 3BInternational Classification and Test Methodology for CommunicationsCablePending CPD Euro-Classes for CablesPCS = gross calorific potentialFIGRA = fire growth rateFS = flame spreadTSP = total smoke production(damaged length)THR = total heat releaseSPR = smoke production rateHRR = heat release rateH = flame spreadPending CPD Euro-Classes for Communications & Energy Cables[A1] EN ISO 1716Mineral Filled Circuit Integrity Cables[B1] FIPEC Sc.2/EN 50265-2-1LCC/HIFT - type LAN Comm. Cables[B2] FIPEC Sc.1/EN 50265-2-1Energy Cables[C] FIPEC Sc.1/EN 50265-2-1High FR/Riser-type Cables[D] FIPEC Sc.1/EN 50265-2-1IEC 332.3C type Cables[E] EN 50265-2-1IEC 332.1/VW1 type Cables[F]No Requirement
TABLE 4Flammability Test Methods and Level of Severity for Wire and CableTest MethodIgnition Source OutputAirflowDurationUL2424/NFPA  8 MJ/kg——259/255/UL723(35,000 BTU/lb.)Steiner Tunnel  88 kW (300 k BTU/hr.)73 m/min.20 min.UL 910/NFPA 262(240 ft/min.) forcedRISER 154 kW (527 K BTU/hr.)Draft30 min.UL2424/NFPA 259Single Burning Item  30 kW (102 k BTU/hr.)36 m3/min.30 min.(20 min burner)Modified IEC 60332-3  30 kW (102 k BTU/hr.) 8 m3/min.20 min.(Backboard behind ladder(heat impact))IEC 60332-320.5 kW (70 k BTU/hr.) 5 m3/min.20 minVertical Tray20.5 kW (70 k BTU/hr.)Draft20 minIEC 60332-1/ULVW-1Bunsen Burner— 1 min(15 sec. Flame)Evolution of Fire Performance (Severity Levels)VW 1/IEC 60332-1/FT-1/CPD Class E(least severe)UL 1581 Tray/IEC 60332-3/FT-2/CPD Class D↓UL 1666 Riser/FT-4/CPD Class C & B2↓NFPA 262/EN 50289/FT-6/CPD Class B1/UL 910↓NFPA 255 & NFPA 259/LC/CPD Class B1+/UL 2424(most severe)
Table 5 indicates requirements for wire and cable that can meet some of the test method criteria as provided in Table 4. “Low smoke and flame compound A” is a fluoropolymer based blend that includes inorganics known to provide proper material properties such that NFPA 255 and NFPA 259 test protocols may be met.
TABLE 5Material Requirements and Properties for Plenum, Riser, and Halogen Free CablesLow Smoke andFlame Compound ALSFR PVC(Halogen Free)(Halogen Free)NFPA 255/259HIFT/NFPA 262IEC 332.2CIEC 332.1PropertiesLCEuro Class B1Class C/DEuro Class ESpecific2.77 g/cc1.65 g/cc1.61 g/cc1.53 g/ccGravityDurometer69/6172/6359/4953/47D Aged,Inst/15 sec.Tensile2,250 psi/15.5 Mpa2,500 psi/1,750 psi/1,750 psi/Strength,17.2 Mpa12.1 Mpa12.1 Mpa20″/min.Elongation,250%180%180%170%20″/min.Oxygen100+% 53% 53% 35%Index,(0.125″)Brittle−46−5−22−15point, deg C.Flexural202000 psi/1400 Mpa56000 psi/390 Mpa41000 psi/280 Mpa49000 psi/340 MPaModulus,0.03″/min.UL Temp125+60  90  75Rating,deg C.Dielectric 2.92 3.25   3.87   3.57Constant,100 MHzDissipation 0.012 0.014   0.015   0.014Factor,100 MHz4pr UTP9–11 mils/.23–.28 mm15–17 mils/.38–.43 mm30–40 mils/.76–1.02 mm20–24 mils/.50–.60 mmJktThickness
Table 6 is provided as an indicator of low acid gas generation performance for various materials currently available for producing wire and cable and cross-web designs of the present invention. The present invention includes special polymer blends that are designed to significantly reduce these values to levels to those shown for low smoke and flame Compound A listed above in Table 5.
TABLE 6Acid Generation Values for Wire and Cable Insulation MaterialsMaterial% AcidPHFEP27.181.72ECTFE23.8901.64PVDF21.482.03LSFR PVC13.781.90Low Smoke and Flame1.543.01Compound A48% LOI HFFR0.353.4234% LOI HFFR.0243.94
Solid flame retardant/smoke suppressed polyolefins may also be used in connection with fluorinated polymers. Commercially available solid flame retardant/smoke suppressed polyolefin compounds all possess dielectric properties inferior to that of FEP and similar fluorinated polymers. In addition, they also exhibit inferior resistance to burning and generally produce more smoke than FEP under burning conditions. A combination of the two different polymer types can reduce costs while minimally sacrificing physio-chemical properties. An additional method that has been used to improve both electrical and flammability properties includes the irradiation of certain polymers that lend themselves to crosslinking. Certain polyolefins are currently in development that have proven capable of replacing fluoropolymers for passing these same stringent smoke and flammability tests for cable separators, also known as “cross-webs”. Additional advantages with the polyolefins are reduction in cost and toxicity effects as measured during and after combustion. The present invention utilizes blends of fluoropolymers with primarily polyolefins as well as the use of “additives” that include C60 fullerenes and compounds that incorporate the fullerenes and substituted fullerenes as well as inorganic clays and metal oxides as required for insulative or semi-conductive properties in addition to the flame and smoke suppression requirements. The use of fluoropolymer blends with other than polyolefins is also a part of the present invention and the incorporation of these other “additives” will be included as the new compounds are created. Reduction of acid gas generation is another key feature provided by the use of these blends as shown in Table 6 and another important advantage presented in the use of the cables and separators of the present invention. Price and performance characteristics for the separators and conduit tubes will determine the exact blend ratios necessary for these compounds.
A high performance communications data cable utilizing twisted pair technology must meet exacting specification with regard to data speed, electrical, as well as flammability and smoke characteristics. The electrical characteristics include specifically the ability to control impedance, near-end cross-talk (NEXT), ACR (attenuation cross-talk ratio) and shield transfer impedance. A method used for twisted pair data cables that has been tried to meet the electrical characteristics, such as controlled NEXT, is by utilizing individually shielded twisted pairs (ISTP). These shields insulate each pair from NEXT. Data cables have also used very complex lay techniques to cancel E and B (electric and magnetic fields) to control NEXT. In addition, previously manufactured data cables have been designed to meet ACR requirements by utilizing very low dielectric constant insulation materials. Use of the above techniques to control electrical characteristics have inherent problems that have lead to various cable methods and designs to overcome these problems. The blends of the present invention are designed such that these key parameters can be met.
Recently, as indicated in Tables 1, 2A and 2B, the development of “high-end” electrical properties for Category 6 and 7 cables has increased the need to determine and include power sum NEXT (near end crosstalk) and power sum ELFEXT (equal level far end crosstalk) considerations along with attenuation, impedance, and ACR values. These developments have necessitated the development of more highly evolved separators that can provide offsetting of the electrical conductor pairs so that the lesser performing electrical pairs can be further separated from other pairs within the overall cable construction.
Recent and proposed cable standards are increasing cable maximum frequencies from 100–200 MHz to 250–700 Mhz. Recently, 10 Gbit over copper high speed standards have been proposed. The maximum upper frequency of a cable is that frequency at which the ACR (attenuation/cross-talk ratio) is essentially equal to 1. Since attenuation increases with frequency and cross-talk decreases with frequency, the cable designer must be innovative in designing a cable with sufficiently high cross-talk. This is especially true since many conventional design concepts, fillers, and spacers may not provide sufficient cross-talk at the higher frequencies. Proposed limits for alien crosstalk have also been added to the present standards as shown in Table 2G. Such limits in many cases can only be met using the separators of the present invention.
Current separator designs must also meet the UL 910 flame and smoke criteria using both fluorinated and non-fluorinated jackets as well as fluorinated and non-fluorinated insulation materials for the conductors of these cable constructions. In Europe, the trend continues to be use of halogen free insulation for all components, which also must meet stringent flammability regulations. The use of the blends of the present invention for both separators and tube conduits will allow for meeting these requirements.
In plenum applications for voice and data transmission, electrical conductors and cables should exhibit low smoke evolution, low flame spread, and favorable electrical properties. Materials are generally selected for plenum applications such that they exhibit a balance of favorable and unfavorable properties. In this regard, each commonly employed material has a unique combination of desirable characteristics and practical limitations. Without regard to flame retardancy and smoke suppressant characteristics, olefin polymers, such as polyethylene and polypropylene, are melt extrudable thermoplastic materials having favorable electrical properties as manifested by their very low dielectric constant and low dissipation factor.
Dielectric constant is the property of an insulation material which determines the amount of electrostatic energy stored per unit potential gradient. Dielectric constant is normally expressed as a ratio. The dielectric constant of air is 1.0, while the dielectric constant for polyethylene is 2.2. Thus, the capacitance of polyethylene is 2.2 times that of air. Dielectric constant is also referred to as the Specific Inductive Capacity or Permittivity.
Dissipation factor refers to the energy lost when voltage is applied across an insulation material, and is the contangent of the phase angle between the voltage and current in a reactive component. Dissipation factor is quite sensitive to contamination of an insulation material. Dissipation factor is also referred to as the Power Factor (of dielectrics).
Fluorinated ethylene/propylene polymers exhibit electrical performance comparable to non-halogenated to olefin polymers, such as polyethylene, but are over 15 times more expensive per pound. Polyethylene also has favorable mechanical properties as a cable jacket as manifested by its tensile strength and elongation to break. However, polyethylene exhibits unfavorable flame and smoke characteristics.
Limiting Oxygen Index (ASTM D-2863) (“LOI”) is a test method for determining the percent concentration of oxygen that will support flaming combustion of a test material. The greater the LOI, the less susceptible a material is to burning. In the atmosphere, there is approximately 21% oxygen, and therefore a material exhibiting an LOI of 22% or more cannot burn under ambient conditions. As pure polymers without flame retardant additives, members of the olefin family, namely, polyethylene and polypropylene, have an LOI of approximately 19. Because their LOI is less than 21, these olefins exhibit disadvantageous properties relative to flame retardancy in that they do not self-extinguish flame, but propagate flame with a high rate of heat release. Moreover, the burning melt drips on the surrounding areas, thereby further propagating the flame.
In the U.S. and Canada, the standards for flame retardancy for voice communication and data communication cables are stringent. The plenum cable test (U.L. 910/CSA FT-6) and riser cable test U.L. 1666 are significantly more stringent than the predominantly used International fire test IEC 332-3, which is similar to the IEEE 383/U.L. 1581 test. Table 4 already summarizes the standards required for various U.L. (Underwriters Laboratories and CSA (Canadian Standards Authority) cable designations.
As indicated above, current separator designs must also meet the UL 910 flame and smoke criteria using both fluorinated and non-fluorinated jackets as well as fluorinated and non-fluorinated insulation materials for the conductors of these cable constructions. The UL 910 criteria has been included in the recently adopted NFPA 262 criteria and extended with more severity in the NFPA 255 and 259 test criteria. To ensure that the test criteria is met, the use of the separators of the current invention is not only useful but often necessary. For meeting the NFPA 72 test criteria for circuit integrity cable, the support-separators and the materials from which they will be produced is an integral part of the present invention. The reduction in material loading (lbs/MFT) as shown in Table 7 can be an essential aspect in meeting this demand. Substantial reduction of this load by the use of separators can be achieved. The use of the polymer blends of the present invention for both separators and conduit tubes will allow for meeting the requirements for not only current circuit integrity cables but also for cables that must meet the newer more stringent requirements in the future.
TABLE 7Insulation Material Criteria For Circuit Integrity CableJacketAp-NumberInsulationThick-CableproximateNominalof Con-AWGThicknessnessDiameterWeightCable Layductorssize(mils)(mils)(in)(lbs/MFT)(in./twist)2163540.34593.72143540.36754.02123550.421064.4
Principal electrical criteria can be satisfied based upon the dielectric constant and dissipation factor of an insulation or jacketing material. Secondarily, the electrical criteria can be satisfied by certain aspects of the cable design such as, for example, the insulated twisted pair lay lengths. Lay length, as it pertains to wire and cable, is the axial distance required for one cabled conductor or conductor strand to complete one revolution about the axis of the cable. Tighter and/or shorter lay lengths generally improve electrical properties.
Individual shielding is costly and complex to process. Individual shielding is highly susceptible to geometric instability during processing and use. In addition, the ground plane of individual shields, 360° in ISTP's—individually shielded twisted pairs is also an expensive process. Lay techniques and the associated multi-shaped anvils of the present invention to achieve such lay geometries are also complex, costly and susceptible to instability during processing and use. Another problem with many data cables is their susceptibility to deformation during manufacture and use. Deformation of the cable geometry, such as the shield, also potentially severely reduces the electrical and optical consistency.
Optical fiber cables exhibits a separate set of needs that include weight reduction (of the overall cable), optical functionality without change in optical properties and mechanical integrity to prevent damage to glass fibers. For multi-media cable, i.e. cable that contains both metal conductors and optical fibers, the set of criteria is often incompatible. The use of the present invention, however, renders these often divergent set of criteria compatible. Specifically, optical fibers must have sufficient volume in which the buffering and jacketing plenum materials (FEP and the like) covering the inner glass fibers can expand and contract over a broad temperature range without restrictions, for example −40 C to 80 C experienced during shipping. It has been shown by Grune, et. al., among others, that cyclical compression and expansion directly contacting the buffered glass fiber causes excess attenuation light loss (as measured in dB) in the glass fiber. The design of the present invention allows for designation and placement of optical fibers in clearance channels provided by the support-separator having multiple shaped profiles. It would also be possible to place both glass fiber and metal conductors in the same designated clearance channel if such a design is required. In either case the forced spacing and separation from the cable jacket (or absence of a cable jacket) would eliminate the undesirable set of cyclical forces that cause excess attenuation light loss. In addition, fragile optical fibers are susceptible to mechanical damage without crush resistant members (in addition to conventional jacketing). The present invention addresses this problem by including the use of both organic and inorganic polymers as well as inorganic compounds blended with fluoropolymers to achieve the necessary properties.
The need to improve the cable and cable separator design, reduce costs, and improve both flammability and electrical properties continues to exist.